Position measuring device

Abstract

To provide a position measuring device capable of removing bias errors contained in a detection signal from a detection section more easily than in the prior art.SOLUTION: A position measuring device includes an imaging unit, a detection unit, a bias correction unit, a position calculation unit, and a rest determination unit. The imaging unit is mounted on a moving body and acquires a captured image of the environment around the moving body. The detection unit is mounted on the moving body, detects the movement of the moving body, and outputs a detection signal indicating the detection result. The bias correction unit processes the detection signal using a correction value that corrects a bias error contained in the detection signal independent of the movement of the moving body. The position calculation unit calculates a position of the moving body based on the captured image acquired by the imaging unit and the detection signal processed by the bias correction unit. The bias correction unit updates a correction value for the bias error based on the detection signal output by the detection unit when the rest determination unit determines that the moving body is at rest.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a position measuring device that measures the position of a moving object. [Background technology]

[0002] Patent Document 1 discloses a calibration method that can calculate and calibrate the zero-point offset of a gyro. The calibration method of Patent Document 1 utilizes dead reckoning that uses the outputs of an acceleration sensor and an angular velocity sensor. To execute the calibration method described in Patent Document 1, it is necessary to install anchors, which are transmitters that transmit anchor IDs, at the first and second points. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-215547 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a position measuring device that can more easily remove bias errors contained in a detection signal from a mounted detector than in the prior art. [Means for solving the problem]

[0005] The position measurement device in the present disclosure is a position measurement device that measures the position of a moving body. The position measurement device includes an imaging unit, a detection unit, a bias correction unit, a position calculation unit, and a stillness determination unit. The imaging unit is mounted on the moving body and captures an image of the environment around the moving body to obtain an image. The detection unit is mounted on the moving body and detects the movement of the moving body and outputs a detection signal indicating the detection result. The bias correction unit processes the detection signal using a correction value that corrects a bias error included in the detection signal independent of the movement of the moving body. The position calculation unit calculates the position of the moving body based on the captured image acquired by the imaging unit and the detection signal processed by the bias correction unit. The stillness determination unit determines whether the moving body is still. The bias correction unit updates the correction value of the bias error based on the detection signal output by the detection unit when the stillness determination unit determines that the moving body is still. Effect of the Invention

[0006] According to the position measuring device of the present disclosure, the bias error contained in the detection signal of the mounted detector can be removed more easily than with conventional techniques. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration of a moving body equipped with a position measurement device according to a first embodiment; [Diagram 2] FIG. 1 is a block diagram showing a configuration of a position measuring device according to a first embodiment. [Diagram 3] FIG. 1 is a schematic diagram illustrating location history data indicating a history of measurement results obtained by a location measurement device according to a first embodiment; [Figure 4] A flowchart showing an example of a bias update process executed by the position measurement device according to the first embodiment. [Diagram 5] A flowchart showing an example of the rest determination process shown in FIG. [Figure 6] A flowchart showing an example of a bias update process executed by the position measurement device according to the second embodiment. [Figure 7]Graph for explaining the operation of the position measuring device according to the second embodiment [Figure 8] A flowchart showing a modification of the bias update process executed by the position measurement device according to the second embodiment. [Figure 9] FIG. 11 is a block diagram showing the configuration of a position measuring device according to a third embodiment. [Figure 10] A flowchart showing an example of a bias update process executed by the position measurement device according to the third embodiment. [Figure 11] A flowchart showing an example of a bias update process executed by the position measurement device according to the fourth embodiment. [Figure 12] A flowchart showing an example of a bias update process executed by the position measurement device according to the fifth embodiment. [Figure 13] 13 is a graph showing a time change of an angular velocity signal, which is an example of an output signal of an IMU of a position measurement device according to a fifth embodiment. [Figure 14] A flowchart showing an example of a bias update process executed by the position measurement device according to the sixth embodiment. [Figure 15] A flowchart illustrating a rest determination process executed by a position measurement device according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] (Background to this disclosure) For example, there is known a position measurement device that is mounted on a moving body such as a manned cargo handling vehicle such as a forklift, an automated guided vehicle (AGV), an autonomously moving baggage transport robot, etc., and measures the position of the moving body using images captured by a camera. As a technology for configuring such a position measurement device, for example, a Visual-SLAM (Simultaneous Localization and Mapping) technology is known that performs self-location measurement and generation of map information based on images captured sequentially.

[0009] The present inventors have studied a technology for improving the measurement accuracy of the position of a moving object by the Visual-SLAM technology by further using an inertial measurement unit (hereinafter, referred to as "IMU"). Here, the detection value output by the IMU includes a bias error that is output independent of the movement of the moving object. For example, a gyro sensor that detects angular velocity, which is an example of an IMU, outputs a non-zero detection value even at the zero point where there is no input value, that is, when there is no rotation. This non-zero detection value is an example of a bias error. The bias error is also called, for example, a zero point bias error, a null bias error, a zero point offset, and a null offset.

[0010] Patent Document 1 discloses a calibration method for calibrating the zero-point offset of a gyro. This calibration method includes a process for determining a difference between a position or angle obtained at a second point by dead reckoning using the output of the acceleration sensor and the angular velocity sensor when a moving body moves from a first point to a second point where the position or angle error is a specific amount and the specific amount, and a process for calculating a zero-point offset, which is a sensor value output by the angular velocity sensor when the moving body is stationary, from the difference obtained as a result of the determination. However, at the first point and the second point, it is necessary to install an anchor, which is a transmitter that transmits an anchor ID, and the mobile terminal is required to wirelessly communicate with this anchor. Therefore, if the anchor is not installed, calibration cannot be performed. If an anchor is installed, it is costly to install it, and the moving body is required to be equipped with a device for wireless communication with the anchor, which makes the configuration complicated.

[0011] Taking into account the problems of the conventional technology, the present inventors have studied the influence of bias error in measuring the position of a moving object, and have devised a position measuring device according to the present disclosure. The position measuring device according to the present disclosure uses the position of the moving object measured by itself to determine whether the moving object is stationary, obtains bias error when stationary, and performs bias update processing. This makes it possible to accurately remove bias error contained in the detection signal of the IMU, and to accurately measure the position of the moving object using the detection result of the IMU. Furthermore, according to the present disclosure, unlike the conventional technology, a position measuring device is obtained that does not require installation of external equipment such as an anchor on the moving path of the moving object to perform bias update processing.

[0012] Hereinafter, the embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or duplicate explanation of substantially the same configuration may be omitted. This is to avoid the following explanation becoming unnecessarily redundant and to facilitate understanding by those skilled in the art.

[0013] The applicant provides the accompanying drawings and the following description so that those skilled in the art can fully understand the present disclosure, and they are not intended to limit the subject matter described in the claims.

[0014] (First embodiment) 1. Configuration 1 is a schematic diagram illustrating a configuration of a moving body 1. A position measurement device 100 according to a first embodiment of the present disclosure is mounted on the moving body 1, such as a manned cargo handling vehicle such as a forklift, an AGV, and an autonomous mobile baggage transport robot, and measures the position of the moving body 1.

[0015] The moving object 1 includes, for example, a platform 1a on which luggage is placed. A position measurement device 100 according to this embodiment is mounted on the moving object 1. The position measurement device 100 includes a camera 2 that captures an image of the surroundings of the moving object 1, and an IMU 3.

[0016] For example, Visual-SLAM technology that measures the self-location and generates map information based on images captured sequentially can be applied to the position measurement device 100. The position measurement device 100 uses not only the images captured by the camera 2 but also the angular velocity signal that is the detection result of the IMU 3 to accurately measure the position of the moving object 1.

[0017] 2 is a block diagram showing the configuration of the position measurement device 100. The position measurement device 100 includes a camera 2, an IMU 3, a control unit 4, a storage unit 5, a communication interface (I / F) 7, and a drive unit 8.

[0018] The camera 2 is an example of an imaging unit of the present disclosure. The camera 2 is mounted on the moving object 1, captures an image of the surroundings of the moving object 1, and generates color image data and distance image data. The camera 2 may include a depth sensor such as an RGB-D camera or a stereo camera. The camera 2 may also be configured with an RGB camera that captures color images and a ToF (Time of Flight) sensor that captures distance images.

[0019] The IMU 3 is an example of a detection unit of the present disclosure. The IMU 3 is mounted on the moving object 1 and detects, for example, the angular velocity of the moving object 1 as motion information indicating the motion of the moving object 1, and outputs a detection signal indicating the detection result.

[0020] The control unit 4 includes a general-purpose processor such as a CPU or MPU that cooperates with software to realize a predetermined function. The control unit 4 realizes various functions such as a position measurement unit 41 and an IMU processing unit 42 by reading and executing a program stored in the storage unit 5, and controls the overall operation of the position measurement device 100. The position measurement unit 41 includes a feature point extraction unit 411, a position calculation unit 414, a map management unit 415, and a stillness determination unit 416. The IMU processing unit 42 includes a bias correction unit 421 and an attitude calculation unit 424. The bias correction unit 421 includes a bias removal unit 422 and a bias update unit 423.

[0021] For example, the control unit 4 executes a program for implementing the position measurement method of the present embodiment or a program for implementing the SLAM algorithm. The control unit 4 is not limited to a unit that implements a predetermined function through the cooperation of hardware and software, and may be configured with a hardware circuit such as an FPGA, an ASIC, or a DSP that is designed as a dedicated circuit for implementing a predetermined function.

[0022] The storage unit 5 is a recording medium for recording various information including programs and data necessary for realizing the functions of the position measuring device 100. The storage unit 5 stores, for example, map information 51 and image data. The storage unit 5 is realized, for example, by a semiconductor memory device such as a flash memory, an SSD, a magnetic storage device such as a hard disk, or other storage devices alone or in appropriate combination thereof. The storage unit 5 may include a volatile memory such as a high-speed SRAM or DRAM for temporarily storing various information. The volatile memory operates, for example, as a working area of ​​the control unit 4 or a frame memory for temporarily storing image data for each frame.

[0023] The communication I / F 7 is an interface circuit that enables communication between the position measurement device 100 and an external device such as an external server via a network. The communication I / F 7 performs communication in accordance with standards such as IEEE802.3 and IEEE802.11.

[0024] The driving unit 8 is a mechanism that moves the moving body 1 according to instructions from the control unit 4. For example, the driving unit 8 includes a driving circuit of an engine connected to tires of the moving body 1, a steering circuit, and a brake circuit.

[0025] 2. Operation The operation of the position measuring device 100 configured as above will be described below.

[0026] 2-1. Position measurement processing 2, an example of a position measurement process will be described as a basic operation of the position measurement device 100. The position measurement process is executed by the control unit 4 operating as a position measurement unit 41.

[0027] First, the control unit 4 obtains data of a plurality of captured images captured at a constant frame rate from the camera 2. Here, the captured images are image data of the environment around the moving object 1 captured by the camera 2.

[0028] Next, the control unit 4 operating as the feature point extraction unit 411 analyzes the captured image to extract feature points. The control unit 4 extracts pixels or pixel groups whose luminance value or color can be distinguished from surrounding pixels or pixel groups as feature points. In order to detect feature points from the captured image, for example, a known FAST (Features from Accelerated Segment Test) technique may be used.

[0029] The control unit 4 performs a process of calculating the position of the moving object 1, as well as a process of creating map information 51. The map information 51 includes information on two-dimensional positions, three-dimensional positions, or both of the two-dimensional positions of the feature points. The control unit 4 operating as the map management unit 415 converts the coordinates of the feature points on the captured image into world coordinates, and registers map points corresponding to the feature points on the captured image in the world coordinate space, thereby creating the map information 51. In the map information 51, a camera frame showing the captured image, and the position and orientation of the camera 2 when the captured image was captured (hereinafter referred to as the "camera pose") are recorded, along with the map points corresponding to the feature points on the captured image. The created map information 51 is stored in the storage unit 5. For example, the control unit 4 can generate the map information 51 by acquiring captured images at predetermined time intervals and registering the feature points while the moving object 1 is moving.

[0030] The control unit 4 operating as the position calculation unit 414 calculates the position of the camera 2 and therefore the position of the moving object 1 using information on the feature points on the captured image extracted by the feature point extraction unit 411 and the map information 51 stored in the storage unit 5. For example, the control unit 4 operating as the position calculation unit 414 performs a feature point matching process for matching the feature points in the captured image with map points in the map information 51, and calculates the camera pose of the camera 2 that captured the captured image. Alternatively, the control unit 4 may use, for example, a known KLT (Kanade-Lucas-Tomasi) tracker technique as the feature point matching process to match the feature points in the previous frame with the feature points in the current frame acquired next to the previous frame.

[0031] The feature point matching process is, for example, a process for determining whether a feature point in a current frame corresponds to a map point in the map information 51 or a feature point in a previous frame based on the feature amount of the feature point. The feature point matching process allows the control unit 4 operating as the position calculation unit 414 to track corresponding feature points among a plurality of captured images sequentially acquired by the camera 2. The feature amount of the feature point is, for example, a SURF feature amount obtained by a SURF (Speed-Up Robust Features) technique, a SIFT feature amount obtained by a SIFT (Scale-Invariant Feature Transform) technique, or an ORB feature amount obtained by an ORB (Oriented FAST and Rotated BRIEF) technique. The feature amount of the feature point is, for example, represented by a vector having one or more dimensions. For example, the SURF feature amount is represented by a 64-dimensional vector, and the SIFT feature amount is represented by a 128-dimensional vector. The similarity of the feature amount is calculated as a distance such as the Euclidean distance between the feature amounts.

[0032] Next, the control unit 4 operating as the position calculation unit 414 calculates a camera pose corresponding to the current frame. The camera pose corresponding to the current frame is calculated based on, for example, a geometric positional relationship between a feature point in the previous frame and a feature point in the current frame. In order to improve the calculation accuracy and / or calculation efficiency of the camera pose corresponding to the current frame, for example, the attitude of the moving body 1 calculated by the attitude calculation unit 424 of the IMU processing unit 42 may be used. The attitude calculation unit 424 can obtain the camera pose corresponding to the previous frame from the position calculation unit 414 and calculate an estimated attitude of the moving body 1 corresponding to the current frame based on the camera pose corresponding to the previous frame and the angular velocity detected by the IMU 3. The position calculation unit 414 obtains the estimated attitude of the moving body 1 corresponding to the current frame calculated by the attitude calculation unit 424 and converts it into a camera pose corresponding to the current frame.

[0033] In this way, by using the angular velocity detected by IMU 3 to estimate the posture of the moving body 1, the position measurement device 100 can efficiently perform feature point matching even when the moving body 1 accelerates or rotates.

[0034] In the position measurement process of this embodiment, the attitude calculation unit 424 in the IMU processing unit 42 operates based on a bias-corrected detection signal obtained by processing the detection signal from the IMU 3 by the bias correction unit 421. In the bias correction unit 421, the bias removal unit 422 performs a process of removing the bias error by subtracting a correction value for the bias error from the detection signal output by the IMU 3. The correction value for the bias error is set in advance as a signal value for offsetting the error contained in the detection signal. The correction value for the bias error is also called a zero point offset and a null offset. The bias update unit 423 performs bias update by setting the correction value for the bias error in the bias removal unit 422 in a bias update process described later.

[0035] The position data of the moving object 1 obtained by the above position measurement process is stored in, for example, an external server or an internal memory of the position measurement device 100, and constitutes position history data indicating the position history of the moving object 1. Such position history data can be used for various data management and data analysis related to the trajectory of the moving object 1 moving within an environment (see FIG. 3). When the position measurement device 100 of this embodiment obtains position history data that accurately measures the trajectory of the moving object 1, the above data management and analysis in, for example, an external server can be made highly accurate.

[0036] 2-2. Bias update process 2-2-1. Operation Overview The position measurement device 100 of this embodiment repeats the bias update process during the position measurement process described above to update the bias error correction value in real time. An overview of the bias update process will be described below with reference to FIG.

[0037] Movement history data by the position measurement device when a mobile body equipped with the position measurement device moves only through a passage extending between two no-entry areas will be described with reference to Figs. 3(a) and 3(b). Fig. 3(a) is a schematic diagram illustrating position history data by a position measurement device operated without long-term bias update. The position history data is stored, for example, in an external server or the like. Fig. 3 shows two-dimensional map data of two no-entry areas 10 and a passage 20 extending between the no-entry areas 10 viewed from above. As shown in Fig. 3(a), when the position measurement device is operated without long-term bias update, the position history data includes a trajectory of erroneous measurement as if the mobile body had mistakenly advanced into the area R surrounded by a dashed line and entered the no-entry area 10. If such erroneous measurement is mixed into the position history data, it will deteriorate the accuracy of data management and analysis in, for example, the above-mentioned external server.

[0038] According to the inventors' intensive research, it was found that the above-mentioned erroneous measurement is caused by the fluctuation of the bias error of the IMU 3 during, for example, position measurement over the trajectory of the moving object 1. The bias error immediately after the start-up of the IMU 3 can be obtained as the average value of the sensor values ​​in a stationary state obtained within a few seconds after the start-up. The bias correction can be performed by subtracting the bias error immediately after the start-up from the subsequent measurement value.

[0039] However, the bias error changes due to external factors such as temperature. Therefore, if the bias correction is performed only immediately after the start of the IMU 3, the bias error will fluctuate when the IMU 3 is continued to operate, and the error included in the detection value of the IMU 3 will become large. If the error included in the detection value of the IMU 3 becomes large, when the detection result of the IMU 3 is used to calculate the camera pose in the position measurement device 100, the camera pose will be calculated incorrectly.

[0040] In response to these problems, the inventors of the present application conducted extensive research and came up with a bias update process that not only acquires the bias error immediately after startup, but also updates the bias error to be removed from the detection signal at appropriate timing while operation continues thereafter.

[0041] Fig. 3(b) is a schematic diagram showing a history of the measurement results of the moving object 1 by the position measurement device 100 when the bias update process of this embodiment is applied. Compared with Fig. 3(a), the position history data in Fig. 3(b) shows a trajectory in which the moving object 1 has moved in the correct direction along the passage 20 indicated by the arrow, without erroneously proceeding into the area R surrounded by the dashed line, as a result of the bias update process. The bias update process according to this embodiment will be described in detail below.

[0042] 2-2-2. Operation details 4 is a flowchart showing an example of the bias update process executed by the position measurement device 100 according to this embodiment. The bias update process is repeatedly executed by the control unit 4.

[0043] First, the control unit 4 determines whether a predetermined period a has elapsed since the last completion of the bias update process (S1). If the predetermined period a has not elapsed (No in S1), the control unit 4 ends the bias update process of FIG. 4 without proceeding to step S2 or later. If the predetermined period a has elapsed (Yes in S1), the control unit 4 operating as the rest-state determination unit 416 performs a rest-state determination process to determine whether the moving object 1 is at rest (S2). For example, the predetermined period a is 1 (s).

[0044] The rest-state determination process S2 of this embodiment is performed by detecting a period during which the moving object 1 has a sufficiently small speed, i.e., a rest period, using the measurement results of the position measurement unit 41 based on Visual-SLAM technology. If the control unit 4 determines that the moving object 1 is stationary, it turns on a rest-state flag indicating the determination result, and if it does not determine that the moving object 1 is stationary, it turns off the rest-state flag. Details of the rest-state determination process S2 will be described later.

[0045] Next, the control unit 4 operating as the bias update unit 423 determines whether the still flag is ON or not (S3). If the still flag is OFF, that is, if the still flag is not ON (No in S3), the control unit 4 ends the bias update process in FIG. 4 without particularly correcting the bias error.

[0046] On the other hand, if the stationary flag is ON (Yes in S3), the control unit 4 operating as the bias update unit 423 acquires, for example, a detection signal output by the IMU 3 during the stationary period (S4), and updates the bias error by setting a correction value for the bias error based on the signal value (S5). The correction value for the bias error is calculated as the average value of the detection signal values ​​of the IMU 3 acquired during a period of several seconds while the vehicle is stationary, for example. Alternatively, in step S4, the control unit 4 acquires the detection signal output from the IMU 3 during the period from the stationary determination time when the stationary flag was turned ON to a time preceding a predetermined time S, and sets the average value of the detection signal values ​​as the correction value for the bias error.

[0047] The bias error is updated by the above-described bias update process. The bias removal unit 422 obtains the updated bias error from the bias update unit 423, and performs bias correction, for example, by subtracting the updated bias error from the subsequent measurement value.

[0048] In this way, the position measurement device 100 can perform the rest determination process S2 using the measurement result of the position of the moving object 1 by the position measurement unit 41, and execute the bias update process to update the bias error in real time (S5). Therefore, not only can the bias error immediately after startup be corrected, but also bias update can be performed to correct the bias while the operation continues thereafter. Therefore, the position measurement device 100 can accurately remove the bias error contained in the detection signal of the IMU 3. The position measurement device 100 can accurately measure the position of the moving object 1 using the detection result of the IMU 3.

[0049] According to the above-described stillness determination process S2, the output value (S4) of the detection signal of the IMU 3 obtained when it is determined that the moving body 1 is still (Yes in S3) is considered to correspond to the bias error and not due to the angular velocity of the moving body 1. Therefore, by detecting such timing, the bias error can be updated (S5) with high accuracy. Details of the stillness determination process S2 in this embodiment will be described below.

[0050] 2-2-3.Stillness determination process Fig. 5 is a flowchart showing an example of the rest-state determination process S2 shown in Fig. 4. First, the control unit 4 operating as the rest-state determination unit 416 measures the rest period p (S21). When starting to measure the rest period p, the rest-state determination unit 416 resets the rest period p and then starts counting up. In the example shown in Fig. 5, the rest period p is a period during which the speed v of the moving object 1 is equal to or less than a predetermined threshold vth set in advance. For example, the threshold vth is 0.075 (m / s).

[0051] For example, after step S21, the rest-state determination unit 416 calculates the speed v of the moving body 1 based on the position data of the moving body 1 output from the position calculation unit 414 (S22). For example, the rest-state determination unit 416 acquires the position data of the moving body 1 output from the position calculation unit 414 at regular time intervals, and calculates the speed v as the magnitude of the amount of change in the position of the moving body 1 per unit time.

[0052] Next, the stillness determination unit 416 determines whether the calculated speed v of the moving object 1 is greater than a threshold vth (S23). The threshold vth is set in advance to indicate, for example, a reference speed at which the moving object 1 is considered to be moving. If the calculated speed v of the moving object 1 is greater than the threshold vth (Yes in S23), the stillness determination unit 416 turns off the stillness flag (S26) and ends the stillness determination process S2. In this case, the moving object 1 is considered to be moving and not stationary, and the bias error is not updated (S5) by proceeding to NO in step S3 of FIG. 4. In this case, the stillness period p is reset, for example, in step S21 in the next loop.

[0053] If the calculated speed v of the moving object 1 is equal to or less than the threshold vth (No in S23), the stationary determination unit 416 determines whether the stationary period p is longer than, for example, a predetermined threshold pth (S24). The threshold pth is set in advance so as to indicate, for example, a reference period during which the moving object 1 is considered to be stationary and stable. Note that the measurement of the stationary period p (S21) may be performed when the process proceeds to No in step S23.

[0054] When the stillness determination unit 416 determines that the stillness period p being measured is equal to or shorter than the threshold pth (No in S24), it turns off the stillness flag (S26), for example, and ends the stillness determination process S2. In this case, unlike the case where the process proceeds to No in step S23, the stillness period p is not reset. On the other hand, when the stillness determination unit 416 determines that the stillness period p is longer than the threshold pth (Yes in S24), it turns on the stillness flag (S25), and ends the stillness determination process S2. In this case, it is considered that the moving object 1 is stably stationary. For this reason, the process proceeds to YES in step S3 of FIG. 4, and the bias error is updated, for example, using the detection signal of the IMU 3 during the stillness period p (S4, S5). For example, the threshold pth is 5 (s).

[0055] As described above, the stationary determination unit 416 calculates the speed v of the moving object 1 based on the measurement result of the position calculation unit 414 (S22), and if the state in which the speed v is equal to or less than the threshold vth continues for the period of the set threshold pth (Yes in S24), it determines that the moving object 1 is stationary (S25). The speed v is calculated as, for example, the amount of change per unit time of the measurement result of the position calculation unit 414.

[0056] 3. Effects etc. As described above, the position measurement device 100 according to this embodiment measures the position of the moving object 1. The position measurement device 100 includes the camera 2, the IMU 3, the bias correction unit 421, the position calculation unit 414, and the stillness determination unit 416. The camera 2 is mounted on the moving object 1 and captures an image of the environment around the moving object 1 to obtain a captured image. The IMU 3 is mounted on the moving object 1 and detects the movement of the moving object 1 and outputs a detection signal indicating the detection result. The bias correction unit 421 processes the detection signal using a correction value that corrects a bias error included in the detection signal of the IMU 3 without depending on the movement of the moving object 1. The position calculation unit 414 calculates the position of the moving object 1 based on the captured image acquired by the camera 2 and the detection signal processed by the bias correction unit. The stillness determination unit 416 determines whether the moving object 1 is still or not (S2). When the rest determination unit 416 determines that the moving object is at rest (Yes in S3), the bias correction unit 421 updates the correction value of the bias error based on the detection signal output by the IMU 3 (S5).

[0057] As a result, the position measurement device 100 can not only correct the bias error immediately after startup, but also update the bias error correction value while the operation continues thereafter to correct the bias error with high accuracy. Therefore, the position measurement device 100 can measure the position of the moving object 1 with high accuracy by using the detection result of the IMU 3.

[0058] Furthermore, unlike the conventional technology, the position measurement device 100 does not need to install an external device such as an anchor on the moving path of the moving object 1 to perform the bias update process. Therefore, the position measurement device 100 can reduce the installation cost of the external device such as an anchor. Also, since the position measurement device 100 does not need to be equipped with a device for wireless communication with the external device such as an anchor, it is possible to prevent the configuration from becoming complicated. In this way, the position measurement device 100 can correct the bias error more easily than the conventional technology.

[0059] The position measuring device 100 may further include a feature point extraction unit 411 that extracts feature points from the captured images acquired by the camera 2. The position calculation unit 414 may calculate the position of the moving object 1 by tracking the feature points extracted by the feature point extraction unit 411 among the multiple captured images sequentially acquired by the camera 2.

[0060] By tracking the features in this manner, the position measuring device 100 can measure the position of the moving object 1 with greater accuracy.

[0061] The stationary determination unit 416 calculates the speed v of the moving body 1 based on the calculation result of the position calculation unit 414, and if the speed v remains below a preset threshold vth (No in S23) for a predetermined period pth (Yes in S24), it determines that the moving body 1 is stationary (S25).

[0062] This makes it possible to prevent the moving body 1 from being determined to be stationary when it stops for only an instant and then resumes moving immediately thereafter, and to determine that the moving body 1 has stopped when it has actually stopped. Therefore, it is possible to prevent the bias error from being calculated assuming that the moving body 1 has stopped when it is not stationary, and it is possible to ensure the accuracy of the bias error calculation.

[0063] Second embodiment The second embodiment will be described below with reference to Figures 6 to 8. In the second embodiment, a position measurement device will be described that relaxes the criteria for determination in the rest state determination process S2 when a period during which the bias has not been updated becomes too long.

[0064] Fig. 6 is a flowchart showing an example of a bias update process executed by the position measurement device according to the second embodiment of the present disclosure. The bias update process in Fig. 6 further includes steps S201 to S203 in addition to the bias update process executed by the position measurement device 100 according to the first embodiment shown in Fig. 4.

[0065] 6, when it is determined in step S1 that the predetermined period a has elapsed (Yes in S1), the control unit 4 determines whether the period during which the bias has not been updated is longer than a predetermined period (S201). The period during which the bias has not been updated is the time that has elapsed since the bias error was last updated. The predetermined period in step S201 is a reference period for which the period during which the bias has not been updated is considered to be too long, and is set to, for example, multiple times the predetermined period a.

[0066] When it is determined that the period during which the bias has not been updated is not long (No in S201), the control unit 4 sets the rest period threshold value pth (see step S24 in FIG. 5) to a normal level value p1 (S202). The normal level value p1 is an initial value that is set, for example, in the same manner as the value of the threshold value pth in the first embodiment. Thereafter, the rest determination process S2 is performed in the same manner as in the first embodiment. On the other hand, when it is determined that the period during which the bias has not been updated is long (Yes in S201), the control unit 4 sets the rest period threshold value pth to a low level value p2 that is smaller than the normal level value p1 (S203), and proceeds to the rest determination process S2. The subsequent steps are the same as in the first embodiment, and therefore description thereof will be omitted.

[0067] Fig. 7 is a graph for explaining the operation of the position measurement device according to this embodiment. The horizontal axis of the graph in Fig. 7 represents time. The vertical axis of the graph in Fig. 7 represents the speed v of the moving object 1 calculated by the rest-state determination unit 416 in step S22.

[0068] As described in FIG. 5 in the first embodiment, the stillness determination unit 416 turns on the stillness flag when the stillness period p during which the speed v of the moving object 1 is equal to or less than the threshold vth is longer than the threshold pth (S23 to S25). If the threshold pth for the stillness period is a normal level value p1, in the moving object 1 moving as shown in the graph of FIG. 7, the stillness period p is shorter than the normal level value p1, so the stillness flag is not turned on and the bias update step S5 is not executed (see step S3 in FIG. 4). If the bias update step S5 is not executed for a long period, the bias error fluctuates and the error included in the detection signal output from the IMU 3 becomes large.

[0069] Therefore, in this embodiment, when it is determined that the period during which the bias has not been updated is long (Yes in S201), the control unit 4 executes step S203 of setting the rest period threshold value pth to the low level value p2 as described above. With this configuration, it is possible to prioritize execution of the bias update step S5 as early as possible when the period during which the bias has not been updated is too long. As a result, for a moving object 1 moving as shown in the graph of FIG. 7, since the rest period p is longer than the period indicated by the low level value p2, the rest flag is turned ON (see steps S24 and S25 in FIG. 5), and the bias update step S5 is executed (see steps S3 to S5 in FIG. 4).

[0070] In the above example, the rest period threshold pth can take only two values, a normal level value p1 and a low level value p2. However, the bias update process in this embodiment is not limited to this, and the control unit 4 may set the rest period threshold pth to a smaller value as the time that has passed since the bias error was last updated increases. For example, the rest period threshold pth may be set to three or more different values ​​depending on the period during which the bias has not been updated. Alternatively, the rest period threshold pth may be set to take continuous values ​​depending on the period during which the bias has not been updated.

[0071] Fig. 8 is a flowchart showing a modified example of the bias update process executed by the position measurement device according to the second embodiment of the present disclosure. Compared with the bias update process of Fig. 6, the bias update process of Fig. 8 includes step S202a instead of step S202 and step S203a instead of step S203. In step S202a, the control unit 4 sets the threshold vth to a normal level value v1. The normal level value v1 is an initial value that is set in the same manner as the value of the threshold vth in the first embodiment, for example. In step S203a, the control unit 4 sets the threshold vth to a high level value v2 that is higher than the normal level value v1.

[0072] The bias update process in this embodiment is not limited to this. For example, similar to the above example in which the threshold pth of the stationary period is changed, the control unit 4 may increase the threshold vth as the time that has passed since the bias error was last updated increases, and the threshold vth may take three or more different values ​​or a continuous value.

[0073] 6 and the bias update process shown in FIG 8 may be performed alone or in combination. For example, when it is determined that the period during which the bias has not been updated is long (Yes in S201), the control unit 4 may set the rest period threshold pth to a low level value p2 and the threshold vth to a high level value v2. In this case, when it is not determined that the period during which the bias has not been updated is long (No in S201), the control unit 4 may set the rest period threshold pth to a normal level value p1 and the threshold vth to a normal level value v1.

[0074] As described above, in this embodiment, the stationary determination unit 416 sets the stationary period threshold pth to a shorter value (S203) and / or sets the threshold vth to a larger value (S203a) as the time that has elapsed since the bias error was last updated increases, and determines whether the moving object is stationary or not (S2).

[0075] In this way, when a long period of time has passed without performing the bias update, at least one of the rest period threshold pth and the rest period threshold vth is changed so that the bias update is performed as soon as possible. Therefore, it is possible to quickly resolve the situation where the bias update is not performed even though the bias error is fluctuating.

[0076] Third embodiment The third embodiment will be described below with reference to Figures 9 to 10. In the third embodiment, a position measuring device using a temperature sensor will be described.

[0077] Fig. 9 is a block diagram showing a configuration of a position measurement device 300 according to a third embodiment of the present disclosure. Compared to the position measurement device 100 according to the first embodiment shown in Fig. 2, the position measurement device 300 in Fig. 9 further includes a temperature sensor 9.

[0078] The temperature sensor 9 detects the temperature of the environment surrounding the moving body 1. The temperature sensor 9 may detect the temperature of the IMU 3. The temperature sensor 9 may be mounted on the moving body 1 and connected directly or indirectly to the control unit 4. Alternatively, the temperature sensor 9 may not be mounted on the moving body 1 and may be installed in the environment surrounding the moving body 1. In this case, the temperature detected by the temperature sensor 9 is transmitted to the control unit 4 by wired or wireless communication. For example, the temperature detected by the temperature sensor 9 may be transmitted to the control unit 4 via a network and the communication I / F 7 of the position measurement device 300.

[0079] Fig. 10 is a flowchart showing an example of a bias update process executed by the position measurement device 300. The bias update process of Fig. 10, compared to the bias update process of Fig. 6, further includes step S300 of acquiring a temperature detection value T, which is a detection result, from the temperature sensor 9, after step S1, for example. Step S300 may be executed when it is determined in step S1 that the predetermined period a has elapsed (Yes in S1), or when it is determined that the predetermined period a has not elapsed (No in S1). Moreover, compared to the bias update process of Fig. 6, the bias update process of Fig. 10 includes step S301 instead of step S201 of determining whether the period in which the bias has not been updated is long.

[0080] In step S301, the control unit 4 uses the temperature detection value T acquired from the temperature sensor 9 to determine whether or not the temperature change amount ΔT, which is the change amount of the temperature detection value T, is greater than a predetermined threshold value Tth. The temperature change amount ΔT is defined as the amount by which the temperature detection value T changes per unit time, for example. If it is determined that the temperature change amount ΔT is equal to or less than the predetermined threshold value Tth (No in S301), the control unit 4 sets the rest period threshold value pth to the normal level value p1 (S202). Thereafter, the rest determination process S2 is performed in the same manner as in the first and second embodiments. If it is determined that the temperature change amount ΔT is greater than the predetermined threshold value Tth (Yes in S301), the control unit 4 sets the rest period threshold value pth to a low level value p2 that is smaller than the normal level value p1 (S203), and proceeds to step S2. The subsequent steps are similar to those in the first and second embodiments, and therefore will not be described.

[0081] In this embodiment, the bias update process performed by the position measurement device 300 may include, instead of or in addition to steps S202 and S203, step S202a of setting the threshold vth to a normal level value v1 and step S203a of setting the threshold vth to a high level value v2 higher than the normal level value v1 (see Figure 8).

[0082] The temperature change amount ΔT is calculated, for example, by the rest state determination unit 416. However, the present embodiment is not limited to this, and the temperature change amount ΔT may be calculated by any functional block of the control unit 4.

[0083] As described above, the position measurement device 300 further includes a temperature sensor 9 that detects the temperature of the environment around the moving object 1. The rest-state determination unit 416 determines whether the moving object 1 is at rest by setting the rest-state period threshold pth shorter and / or setting the threshold vth larger as the change in temperature detected by the temperature sensor 9 increases.

[0084] One of the causes of the bias error varying from that immediately after startup is a change in temperature of the surrounding environment. When the change in temperature detected by the temperature sensor 9 is large, the bias error is likely to vary. Therefore, the position measurement device 300 according to this embodiment changes at least one of the rest period threshold pth and the threshold vth so that the bias update is performed as soon as possible when the change in temperature detected by the temperature sensor 9 is large. Therefore, it is possible to quickly resolve a situation in which the bias update is not performed even though the bias error is varying.

[0085] (Fourth embodiment) The fourth embodiment will be described below with reference to Fig. 11. In the second embodiment, the judgment criteria for the rest-state judgment process S2 are relaxed when the period during which the bias has not been updated becomes too long. In this embodiment, a position measurement device is described in which the cycle a of the bias update process is shortened instead of the judgment criteria for the rest-state judgment process S2.

[0086] Fig. 11 is a flowchart showing an example of a bias update process executed by the position measurement device according to the fourth embodiment of the present disclosure. The bias update process in Fig. 11 further includes steps S401 to S403 in addition to the bias update process executed by the position measurement device 100 according to the first embodiment shown in Fig. 4.

[0087] Unlike FIG. 4, in FIG. 11, if it is determined in step S3 that the stationary flag is OFF (No in S3), the control unit 4 determines whether the period during which the bias has not been updated is long (S401), for example, similar to step S201 in the second embodiment.

[0088] When it is determined that the period during which the bias has not been updated is not long (No in S401), the control unit 4 sets the period a to a normal value (S402). On the other hand, when it is determined that the period during which the bias has not been updated is long (Yes in S401), the control unit 4 sets the period a to a value shorter than the normal value (S403) and ends the processing in Fig. 11. The bias update processing in Fig. 11 is repeatedly executed by the control unit 4. Therefore, in step S1 in the next loop after the period a is set to a short value in step S402, the control unit 4 determines whether the reset and shortened period a has elapsed since the last completion of the bias update processing.

[0089] As a result, for example, in the initial setting, the period a is 5 minutes and the rest determination step S2 is executed once every 5 minutes, but if the bias is not updated for a long period of time (Yes in S401), the period a is shortened by resetting it to 1 minute (S402), and thereafter the rest determination step S2 is executed once every minute.

[0090] As described above, the stationary state determination unit 416 determines whether the moving object 1 is stationary or not for each preset period a. The period a is set to be shorter as the time that has elapsed since the bias error was last updated is longer (S402).

[0091] Even if the vehicle is in a state where it would be determined that the vehicle is stationary if a stillness determination was performed, the stillness determination is not performed and the stillness flag is not turned ON unless the period a has elapsed since the last time the stillness determination was performed. In this embodiment, if a long time has elapsed since the last time the bias error was updated, the period a is shortened to increase the frequency of stillness determination. This increases the number of opportunities to determine that the vehicle is stationary, and it is possible to quickly resolve a situation where the bias update is not performed even though the bias error is fluctuating.

[0092] Fifth embodiment Hereinafter, the fifth embodiment will be described with reference to Figures 12 and 13. In this embodiment, a position measurement device that uses the variation in the detection signal of the IMU 3 to determine whether or not to update the bias will be described.

[0093] Fig. 12 is a flowchart showing an example of a bias update process executed by the position measurement device according to the fifth embodiment of the present disclosure. The bias update process in Fig. 12 further includes step S500 in addition to the bias update process executed by the position measurement device 100 according to the first embodiment shown in Fig. 4.

[0094] Step S500 is executed between steps S4 and S5 by the control unit 4 operating as, for example, the bias update unit 423 of the bias correction unit 421. In step S500, the control unit 4 determines whether or not the variance V of the output signal of the IMU 3 is greater than, for example, a predetermined threshold value Vth. If it is determined that the variance V is large (Yes in S500), the control unit 4 operating as the bias update unit 423 ends the process without executing the bias update step S5. If it is not determined that the variance V is large (No in S500), the control unit 4 operating as the bias update unit 423 executes the bias update step S5.

[0095] Fig. 13 is a graph showing a time change of an angular velocity signal, which is an example of an output signal of the IMU 3. In the flow of Fig. 12, when it is determined in step S3 that the stationary flag is ON, the control unit 4 operating as the bias update unit 423 acquires a detection signal output by the IMU 3 (S4). Next, the control unit 4 acquires a detection signal output from the IMU 3 during a period from the stationary determination time when the stationary flag is ON to a time point going back a predetermined time S, and calculates a variance V of the detection signal value. In step S500, the control unit 4 determines, for example, whether the calculated variance V is greater than a predetermined threshold value Vth.

[0096] FIG. 13(a) shows that the variance of the angular velocity signal output from the IMU 3 during the period from the time when the vehicle was determined to be stationary to a time point preceding a predetermined time S is V1, and FIG. 13(b) shows that this variance is V2. Here, V1<Vthであり、V2> 13(a), if the variance V1 is smaller than the predetermined threshold Vth, the process proceeds to No in step S500, and the control unit 4 operating as the bias update unit 423 executes the bias update step S5. On the other hand, if the variance V2 is larger than the predetermined threshold Vth, as in FIG. 13(b), the process proceeds to Yes in step S500, and the control unit 4 operating as the bias update unit 423 does not execute the bias update step S5.

[0097] As described above, the bias correction unit 421 determines whether or not to update the bias error (S500) based on the variance V of the values ​​of the detection signals output by the IMU 3. For example, when the variance V of the values ​​of the detection signals output by the IMU 3 is greater than a predetermined threshold Vth, the bias correction unit 421 determines not to update the bias error.

[0098] This makes it possible to calculate the bias error and update the bias using the reliable detection signal value of IMU3, which has a small variance V, and therefore allows the bias error to be corrected more accurately.

[0099] Sixth embodiment Hereinafter, the sixth embodiment will be described with reference to Fig. 14. In this embodiment, a position measurement device that uses a feature point in position calculation to determine whether or not to update the bias will be described.

[0100] Fig. 14 is a flowchart showing an example of a bias update process executed by the position measurement device according to the sixth embodiment of the present disclosure. The bias update process in Fig. 14 further includes steps S601 and S602 between steps S1 and S2 in addition to the bias update process executed by the position measurement device 100 according to the first embodiment shown in Fig. 4.

[0101] In step S601, for example, the stillness determination unit 416 acquires feature point data from the feature point extraction unit 411. The feature point data is, for example, data indicating the coordinates of all feature points in the captured image. The stillness determination unit 416 calculates the number of feature points present in the captured image based on the feature point data. Alternatively, the stillness determination unit 416 may acquire the number of feature points from the feature point extraction unit 411 as the feature point data.

[0102] In step S602, which is the next step after step S601, the stillness determination unit 416 determines whether or not the number of feature points in the captured image is sufficiently large. For example, when the number of feature points in the captured image is equal to or greater than a predetermined threshold, the stillness determination unit 416 determines that the number of feature points in the captured image is sufficiently large. If it is determined that the number of feature points is sufficiently large (Yes in S602), the process proceeds to stillness determination process S2. If it is not determined that the number of feature points is sufficiently large (No in S602), the control unit 4 ends the bias update process in FIG. 14 and does not execute bias update step S5. The subsequent steps are the same as those in the first embodiment, and therefore will not be described.

[0103] Although an example has been described in which step S601 for acquiring feature point data and step S602 for determining whether the number of feature points is sufficiently large are executed between steps S1 and S2, the present embodiment is not limited to this. For example, steps S601 and S602 may be executed immediately before the bias update step S5.

[0104] As described above, the position measurement device may further include a feature point extraction unit 411 that extracts feature points from a captured image acquired by the camera 2. If the number of feature points extracted by the feature point extraction unit is less than a predetermined number (No in S602), the bias correction unit 421 does not update the bias error.

[0105] When the number of feature points is not sufficiently large, the accuracy of the calculation of the position of the moving body 1 by the position calculation unit 414 and the accuracy of the stillness determination by the stillness determination unit 416 based on the calculated position of the moving body 1 are not high, and the reliability of these processes is not guaranteed. In this embodiment, when the reliability of the position calculation process, the stillness determination process, etc. is not guaranteed in this way, the bias update step S5 is not executed, and it is possible to prevent the bias error from being updated to a value with low reliability.

[0106] (Other embodiments) As described above, the first to sixth embodiments have been described as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are appropriately performed. In addition, it is also possible to combine the components described in the first to sixth embodiments to create new embodiments.

[0107] Therefore, other embodiments will be exemplified below. In the stillness determination process (S2) of the first embodiment shown in FIG. 5, step S22 for calculating the speed v of the moving body 1 based on the position of the moving body 1 has been described, and the process for determining whether to turn the stillness flag ON or OFF based on whether the calculated speed v is greater than a threshold vth has been described. The stillness determination unit 416 of the position measurement device according to the present disclosure is not limited to calculating the speed v of the moving body 1 based on the position of the moving body 1 as long as it determines whether the moving body 1 is still or not. For example, the stillness determination unit 416 compares the position of a feature point in the previous frame with the position of a feature point in the current frame corresponding to this feature point to calculate the amount of movement of the feature point from the previous frame to the current frame, and determines that the moving body 1 is still when the average movement amount d, which is the average value of the movement amount for each feature point, is equal to or less than a predetermined threshold dth. That is, when the difference between the images of the previous frame and the current frame is small, it is determined that the camera 2 and therefore the moving body 1 are still. This allows the stillness determination to be performed without calculating the speed v of the moving body 1, so that the processing load on the control unit 4 can be reduced and the stillness determination can be performed at high speed.

[0108] Fig. 15 is a flowchart illustrating a rest-state determination process executed by a position measurement device according to such another embodiment. Compared to the rest-state determination process of the first embodiment shown in Fig. 5, the rest-state determination process of Fig. 15 includes step S701 instead of step S22 and step S702 instead of step S23.

[0109] In step S701, the stillness determination unit 416 calculates an average movement amount d of feature points from the previous frame to the current frame. Next, in step S702, the stillness determination unit 416 determines whether or not the average movement amount d is greater than a predetermined threshold dth. If the average movement amount d is greater than the predetermined threshold dth (Yes in S702), the stillness determination unit 416 turns off the stillness flag (S26) and ends the stillness determination process. If the average movement amount d is equal to or less than the predetermined threshold dth (No in S702), the process proceeds to step S24. The subsequent steps are the same as those in the first embodiment, and therefore will not be described.

[0110] In the above embodiment, an example has been described in which the IMU 3, which is an example of a detection unit, detects the angular velocity of the moving body 1 and outputs a detection signal indicating the detection result. The IMU 3 may be any device that detects motion information indicating the motion of the moving body 1, and may be, for example, an acceleration sensor. For example, the control unit 4 operating as the bias update unit 423 acquires (S4) a detection signal output by the acceleration sensor when the stationary flag is ON (Yes in S3 of FIG. 4), and updates the bias error by setting a correction value for the bias error based on the signal value (S5). For example, a bias of 1 g (m / s 2 In this case, the control unit 4 calculates the bias error correction value assuming that a gravitational acceleration of 1g (m / s 2 ) and use the calculated difference as the bias error correction value. In this case, the control unit 4 may calculate the bias error correction value for the horizontal component by regarding the acceleration component in the horizontal direction (x direction and y direction) perpendicular to the vertical direction as zero.

[0111] In the above embodiment, an example was described in which the IMU detection result is used as an auxiliary means for increasing the accuracy of the camera pose calculation. In this embodiment, the method of using the IMU detection result is not limited to this, and for example, the IMU detection result may be used to calculate the camera pose only from the IMU detection result when a loss occurs. Here, the term "lost" means that the number of feature points that have been successfully matched is not equal to or greater than a predetermined threshold, or that the position measurement device is unable to calculate the camera pose based on the geometric positional relationship between the feature points in the frame before the previous frame and the feature points in the current frame.

[0112] In the above embodiment, the position measurement device 100 is described as being used to accumulate position history data of the moving object 1. In this embodiment, the use of the position measurement device 100 is not limited to the above, and the position measurement device 100 may be applied to, for example, driving control of the moving object 1. In such a use, the accuracy of driving control of the moving object 1 can be improved, for example, by updating the bias error in real time as in the above embodiment.

[0113] As described above, the embodiments have been described as examples of the technology in the present disclosure, and the accompanying drawings and detailed description have been provided for this purpose.

[0114] Therefore, among the components described in the attached drawings and the detailed description, not only are there components essential for solving the problem, but there may also be components that are not essential for solving the problem in order to illustrate the above technology. Therefore, the fact that such non-essential components are described in the attached drawings or the detailed description should not be interpreted as immediately indicating that such non-essential components are essential.

[0115] Furthermore, since the above-described embodiments are intended to illustrate the technology in the present disclosure, various modifications, substitutions, additions, omissions, and the like can be made within the scope of the claims or their equivalents. [Industrial Applicability]

[0116] The present disclosure is applicable to a position measuring device that measures the position of a moving object. [Explanation of symbols]

[0117] 1. Mobile 2 Camera 4. Control section 41 Position measurement section 411 Feature Point Extraction Unit 414 Position calculation part 415 Map Management Department 416 Stationary judgment section 42 Processing section 421 Bias correction unit 422 Bias Removal Section 423 Bias Update Unit 424 Posture calculation section 5 Storage section 51 Map Information 7 Communication I / F 8 Drive unit 9 Temperature Sensor 10 No entry area 20 Passage 100 Position Measuring Device

Claims

1. A position measuring device for measuring a position of a moving object, comprising: an imaging unit mounted on the moving body and configured to capture an image of an environment surrounding the moving body; a detection unit mounted on the moving body, which detects a motion of the moving body and outputs a detection signal indicating a detection result; a bias correction unit that processes the detection signal using a correction value that corrects a bias error included in the detection signal without depending on the movement of the moving object; a position calculation unit that calculates a position of the moving object based on the captured image acquired by the imaging unit and the detection signal processed by the bias correction unit; a stationary determination unit that determines whether the moving object is stationary, The bias correction unit updates a correction value for the bias error based on a detection signal output by the detection unit when the rest determination unit determines that the moving body is at rest.

2. The imaging device further includes a feature point extraction unit that extracts feature points from the captured image acquired by the imaging unit, The position measuring device according to claim 1 , wherein the position calculation unit calculates the position of the moving object by tracking the feature points extracted by the feature point extraction unit among a plurality of captured images sequentially acquired by the imaging unit.

3. The imaging device further includes a feature point extraction unit that extracts feature points from the captured image acquired by the imaging unit, The position measuring device according to claim 1 , wherein the bias correction unit does not update the bias error when the number of feature points extracted by the feature point extraction unit is less than a predetermined number.

4. The rest determination unit is Calculating a speed of the moving object based on a calculation result of the position calculation unit; 4. The position measuring device according to claim 1, wherein the moving body is determined to be stationary when the speed remains equal to or less than a preset threshold for a predetermined period of time.

5. The position measuring device according to claim 4 , wherein the stationary determination unit determines whether the moving body is stationary by setting the specified period to be shorter and / or the threshold to be larger the longer the time that has elapsed since the bias error was last updated.

6. A temperature sensor is further provided to detect a temperature of an environment surrounding the moving body, The position measuring device according to claim 4 or 5, wherein the rest-state determination unit determines whether the moving body is at rest by setting the specified period shorter and / or the threshold value larger as the change in temperature detected by the temperature sensor becomes greater.

7. the stationary determination unit determines whether the moving object is stationary at every preset period, 7. The position measuring device according to claim 1, wherein the period is set to be shorter as the time that has elapsed since the bias error was last updated is longer.

8. A temperature sensor is further provided to detect a temperature of an environment surrounding the moving body, The position measurement device according to claim 7 , wherein the rest-state determination unit determines whether or not the moving body is at rest by setting the period to be shorter as the change in temperature detected by the temperature sensor becomes larger.

9. 9. The position measuring device according to claim 1, wherein the bias correction unit determines whether or not to update the bias error based on a variance of the value of the detection signal output by the detection unit.

10. 10. The position measuring device according to claim 1, wherein the detection unit includes a gyro sensor that detects an angular velocity as the movement of the moving body.

Images